CN110621556B - Vehicle braking system using electric parking brake under boost failure condition - Google Patents

Abstract

A braking system for a vehicle, comprising: a driver-operable brake pedal coupled to control the brake pressure generating unit to supply hydraulic brake pressure to front and rear hydraulically-driven wheel brakes, wherein the rear wheel brakes are also configured to be electrically driven; sensor means for monitoring driver braking intent; the brake system is operable in a first mode in which both the front and rear brakes are hydraulically actuated, and a second mode in which the front brake is hydraulically actuated but the rear brake is electrically actuated, the rear brake including a brake caliper assembly including a brake pad operable to engage the brake rotor to brake the vehicle, the brake caliper assembly including a hydraulic drive mechanism and an electric drive mechanism, a controller connected to the sensor arrangement for operating the electric drive mechanism to drive the rear brake in accordance with a driver's braking demand.

Description

Vehicle braking system using electric parking brake under boost failure condition

Cross Reference to Related Applications

Priority and benefit of U.S. provisional application serial No. 62/464,957 filed on 28.2.2017, U.S. provisional application serial No. 62/611,906 filed on 29.12.12.2017, U.S. provisional application serial No. 62/611,909 filed on 29.12.12.2017, and U.S. provisional application serial No. 62/611,916 filed on 29.12.2017, the entire disclosures of which are incorporated herein by reference.

Technical Field

The present invention relates generally to hydraulic booster brake systems and, more particularly, to methods of operating an electric parking brake for use with such hydraulic booster brake systems.

Background

One example of a prior art hydraulic booster brake system that uses an Electric Parking Brake (EPB) as a backup in the event of a failure is disclosed in U.S. patent No.6,598,943 to Harris, the disclosure of which is incorporated herein by reference in its entirety. In prior art systems, a vehicle brake system is provided that includes an electro-hydraulic brake device and an electric parking brake device.

The electro-hydraulic brake devices are of the type having a normal boost operating mode in which pressurized hydraulic fluid pressure is applied at the wheels by a braking device (e.g., a disc brake) in proportion to the driver's braking demand to provide service braking. Braking demand is electronically sensed at the service brake pedal. If the boosted operating mode fails, the system operates in a propulsion mode to provide service braking. In the propulsion mode, service braking is provided by hydraulic fluid pressure applied to the braking devices through a master cylinder mechanically coupled to a service brake pedal.

The electric parking brake provides a parking brake function using a brake device. In the event of a failure of the boost operating mode, for example where boost has failed or is unavailable, scheduling operation of the service brake pedal by the driver also results in operation of the electric parking brake to supplement the braking provided by the propulsion mode.

In the system of us patent No.6,598,943, the propulsion mode operates only on the brakes of the front wheels, while the electric parking brake operates only on the rear wheels. However, because the electric parking brake is not designed for applying a precisely known brake torque, there is still some risk that using the electric parking brake to supplement the propulsion mode may cause instability by locking the rear wheels. Us patent No.6,598,943 addresses this problem by arranging the system layout so that wheel speed data is available to the parking brake electronic control unit. Electronic brake distribution (EBA) technology can thus be used so that if the rear wheels tend to lock, the electric parking brake is released and then reapplied at a lower torque level. Alternatively, the electric parking brake may be controlled in a manner similar to an anti-lock brake system (ABS), i.e., by cyclically applying and releasing the electric parking brake in response to wheel speed data.

However, in the propel mode, the service brake pedal has a significant stroke before the electric parking brake provides the desired braking force. The driver may find that a significant travel of the service brake pedal is an alarm. Furthermore, restricting the propulsion mode to operate only on the brakes on the front wheels requires isolating the hydraulic brake circuit from the brakes on the rear wheels. However, isolating the hydraulic brake circuit from the brakes of the rear wheels may result in air being drawn into the hydraulic circuit when the electric parking brake is operated. Accordingly, there is a need to improve operation of an electric parking brake when the electric parking brake is operated to supplement a propulsion mode of a hydraulic booster system in the event of a boost failure condition.

Disclosure of Invention

The present invention relates to a method of operating an electric parking brake for use as a backup in a hydraulic booster brake system configured to provide four-wheel propulsion in a failed boost condition. According to the present invention, an electric parking brake is driven to provide a braking torque coverage at a wheel where the electric parking brake is installed. The brake torque overlay is a function of the driver's operation of the service brake pedal of the vehicle.

According to one embodiment, a vehicle braking system for a vehicle may comprise one or more of the following features, alone and/or in combination: a brake pedal operable by a vehicle driver and coupled to control a brake pressure generating unit to supply hydraulic brake pressure to front and rear hydraulically-driven wheel brakes, wherein the rear wheel brakes are also configured to be electrically driven; sensor means for monitoring driver braking intent; the brake system is operable in a first mode in which both the front and rear brakes are hydraulically actuated, and a second mode in which the front brake is hydraulically actuated but the rear brake is electrically actuated, the rear brake including a brake caliper assembly including a brake pad operable to engage the brake rotor to brake the vehicle, the brake caliper assembly including a hydraulic drive mechanism and an electric drive mechanism, a controller connected to the sensor arrangement for operating the electric drive mechanism to drive the rear brake in accordance with a driver's braking demand.

According to this embodiment, the sensor device monitors the brake pedal travel and the electric drive mechanism is operated in dependence on the brake pedal travel.

According to this embodiment, the sensor device monitors the brake pedal force applied by the driver and/or the hydraulic pressure in the unit, and the electric drive mechanism is operated in dependence on the pedal force and/or the hydraulic pressure.

According to this embodiment, the electric operating mechanism operates according to a predetermined drive time profile which is a function of the pedal force and/or the hydraulic pressure.

According to this embodiment, the controller is responsive to an initial braking command to operate the electric drive mechanism such that the brake pads are moved to the disc contact position.

According to this embodiment, the initial brake command is a function of the travel of the brake pedal when initially operated by the vehicle driver.

According to this embodiment, the vehicle includes a vehicle accelerator pedal operable by a vehicle driver to control propulsion of the vehicle, and wherein the initial braking command is a function of the driver's accelerator pedal release rate.

According to this embodiment, the brake system includes at least one inlet or isolation valve connected to supply pressure to the hydraulic drive mechanism, and the controller is operable to drive the isolation valve to hydraulically isolate the front brakes from the rear brakes when the system is in the second mode.

According to this embodiment, the brake system includes at least one outlet or bleed valve connected to release pressure from the hydraulic drive mechanism, and the controller is operable to actuate the bleed valve during at least a portion of the time that the electric drive mechanism is operating to prevent hydraulic lock and/or vacuum pull in the hydraulic drive mechanism.

According to this embodiment, the brake system is a brake-by-wire system, wherein the first mode defines a brake-by-wire boost mode and the second mode defines a manual propulsion boost failure mode.

According to this embodiment, the electric drive mechanism also forms part of an electric parking brake system.

Other advantages of the present invention will become apparent to those skilled in the art from the following detailed description of the preferred embodiments, when read in light of the accompanying drawings.

Drawings

FIG. 1 is a schematic diagram of a service brake system and an electric parking brake for a vehicle.

Fig. 2 is a cross-sectional view of a wheel brake of the service brake system of fig. 1 with an electric parking brake of fig. 1.

Fig. 3 is a flowchart of a first embodiment of a control method for the electric parking brake of fig. 1.

Fig. 4A and 4B are tables and graphs of the control method of fig. 3.

FIG. 5 is a flow chart of a lash reduction method for use with the control method of FIG. 3.

FIG. 6 is a flow chart of a pressure relief method for use with the control method of FIG. 3.

Fig. 7 is a schematic flow diagram of the control method of fig. 3 in combination with the methods of fig. 5 and 6 and the tables and graphs of fig. 4A and 4B.

Fig. 8 is a flowchart of a second embodiment of a control method for the electric parking brake of fig. 1.

FIG. 9 is a state diagram for the electric parking brake of FIG. 1 during the control method of FIG. 8.

Fig. 10A and 10B are a first table and a chart for the control method of fig. 8.

Fig. 11A and 11B are a second table and a chart for the control method of fig. 8.

Fig. 12 is a schematic flow chart of the control method of fig. 8 in conjunction with the methods of fig. 5 and 6 and the tables and graphs of fig. 10A-11B.

Detailed Description

Referring now to the drawings, a service braking system, generally designated 100, incorporating features of the present invention is schematically illustrated in FIG. 1. The service braking system 100 may be as disclosed in U.S. patent No.9,321,444 to Ganzel, the disclosure of which is incorporated herein by reference in its entirety.

The service brake system 100 is a hydraulic booster brake system. The pressurized fluid pressure is used to apply a service braking force to the service braking system 100. Preferably, the fluid pressure is hydraulic brake fluid pressure. The service braking system 100 may suitably be used on a land vehicle, such as a motor vehicle having four wheels, with a wheel brake associated with each wheel. In addition, the service brake system 100 may be provided with other braking functions, such as anti-lock braking (AB) and other slip control features, to effectively brake the vehicle.

The service brake system 100 generally includes a first module or brake pedal unit assembly, represented by dashed line 102, and a second module or hydraulic control unit, represented by dashed line 104. The various components of the service brake system 100 are housed in a brake pedal unit assembly 102 and a hydraulic control unit 104. The brake pedal unit assembly 102 and the hydraulic control unit 104 may include one or more modules or housings made of a solid material, such as aluminum, that have been drilled, machined, or otherwise formed to accommodate various components. Fluid conduits may also be formed in the housing to provide fluid communication between the various components. The housing of the brake pedal unit assembly 102 and the hydraulic control unit 104 may be a single structure or may be made of two or more parts assembled together.

As schematically shown, hydraulic control unit 104 is located remotely from brake pedal unit assembly 102, with hydraulic lines hydraulically coupling brake pedal unit assembly 102 and hydraulic control unit 104. Alternatively, the brake pedal unit assembly 102 and the hydraulic control unit 104 may be housed in a single housing. It should also be understood that the grouping of components shown in FIG. 1 is not intended to be limiting, and that any number of components may be housed in any one housing.

The brake pedal unit assembly 102 is used in cooperation with the hydraulic control unit 104 to actuate first, second, third and fourth wheel brakes (generally indicated at 106A, 106B, 106C and 106D, respectively) to provide service braking for the vehicle. First wheel brake 106A, second wheel brake 106B, third wheel brake 106C, and fourth wheel brake 106D may each be any suitable wheel brake configuration that is operated by the application of pressurized brake fluid. As will be discussed with respect to fig. 2, the first, second, third and fourth wheel brakes 106A, 106B, 106C, 106D include a brake piston 310 and a brake caliper assembly 302 (all shown in fig. 2) mounted on the vehicle, respectively. The brake piston 310 and the brake caliper assembly 302 engage the brake rotor 304 (shown in fig. 2), which rotates with the associated wheel to effect braking of the wheel 304.

First wheel brake 106A, second wheel brake 106B, third wheel brake 106C, and fourth wheel brake 106D are associated with any combination of front and rear wheels, respectively, of a vehicle in which service brake system 100 is installed. For example, for a vertical disconnect system, the first wheel brake 106A and the fourth wheel brake 106D may each be associated with a wheel on the same axle. For a diagonally separated braking system, first wheel brake 106A and second wheel brake 106B may be associated with the front wheels, respectively. Preferably, the first wheel brake 106A and the second wheel brake 106B are used for the front wheels of the vehicle, respectively, and the third wheel brake 106C and the fourth wheel brake 106D are used for the rear wheels of the vehicle, respectively.

The brake pedal unit assembly 102 includes a fluid reservoir 108 for storing and holding hydraulic fluid for the service brake system 100. The hydraulic fluid within the fluid reservoir 108 may generally be maintained at atmospheric or other pressure, if desired. The service braking system 100 may include a fluid level sensor 110 for detecting a fluid level of the reservoir. The fluid level sensor 110 may help determine whether a leak has occurred in the service braking system 100.

The brake pedal unit assembly 102 includes a Brake Pedal Unit (BPU), generally indicated by reference numeral 112. It should be understood that the structural details of the components of the brake pedal unit 112 illustrate only one example of the brake pedal unit 112. Brake pedal unit 112 also includes an input piston 114, a primary piston 116, and a secondary piston 118. A service brake pedal (shown schematically at 120 in fig. 1) is coupled to a first end of the input piston 114 via an input rod 122. The input rod 122 may be directly coupled to the input piston 114 or may be indirectly connected through a coupler (not shown). Brake pedal unit 112 is in a "rest" position as shown in FIG. 1. In the "at rest" position, service brake pedal 120 is not depressed by the vehicle operator.

The brake pedal unit 112 is in fluid communication with the fluid reservoir 108 via a conduit 124. Brake pedal unit 112 is also in fluid communication with a simulation valve 126 via a conduit 128. The analog valve 126 may be a shut-off valve that may be electrically operated. The analog valve 126 may be mounted in the housing of the brake pedal unit 112 or may be remote from the housing of the brake pedal unit 112. The brake pedal unit 112 houses various components defining a pedal simulator assembly, generally indicated by the numeral 130, and a fluid simulation chamber 132. The fluid simulation chamber 132 is in fluid communication with a conduit 134, which conduit 134 is in turn in fluid communication with the simulation valve 126.

As described above, the brake pedal unit 112 includes the primary piston 116 and the secondary piston 118, respectively. Primary piston 116 and secondary piston 118, respectively, are generally coaxial with one another. The primary output conduit 136 is in fluid communication with the primary piston 116. Secondary output conduit 138 is in fluid communication with secondary piston 118. As will be discussed in detail below, primary piston 116 and secondary piston 118 move rightward (as viewed in FIG. 1), respectively, to provide pressurized fluid through primary output conduit 136 and secondary output conduit 138, respectively. The rightward movement of the second piston 118 (as viewed in fig. 1) also causes a pressure buildup in the secondary output pressure chamber 140. The secondary output pressure chamber 140 is in fluid communication with the secondary output conduit 138 such that pressurized fluid is selectively provided to the hydraulic control unit 104. The rightward movement of the master piston 116 (as viewed in fig. 1) results in a pressure buildup in the master output pressure chamber 142. The primary output pressure chamber 142 is in fluid communication with the primary output conduit 136 such that pressurized fluid is selectively provided to the hydraulic control unit 104.

The service braking system 100 may also include a stroke sensor (shown schematically at 144 in FIG. 1) for generating a pedal stroke signal indicative of a stroke length or percentage of the input piston 114. The stroke length of input piston 114 also represents the pedal stroke of service brake pedal 120. The service brake system 100 may also include a switch 146 for generating a signal for actuating a brake light and providing a signal indicative of movement of the input piston 114. Service braking system 100 may also include sensors, such as a first pressure sensor 148 and a second pressure sensor 150, for monitoring the pressure in primary output conduit 136 and secondary output conduit 138, respectively.

The service braking system 100 also includes a pressure source in the form of a plunger assembly, generally indicated by reference numeral 152. The plunger assembly 152 is a brake pressure generating unit. As will be explained in detail below, the service braking system 100 uses the plunger assembly 152 to provide the required pressure levels to the first, second, third and fourth wheel brakes 106A, 106B, 106C and 106D, respectively, during normal booster brake application. Fluid from the first, second, third, and fourth wheel brakes 106A, 106B, 106C, 106D, respectively, may be returned to the plunger assembly 152 or diverted to the fluid reservoir 108.

The service braking system 100 also includes a first isolation valve 154 and a second isolation valve 156 (otherwise commonly referred to in the art as a switching valve or a base brake valve). The first and second isolation valves 154, 156 may each be solenoid-driven three-way valves. The first and second isolation valves 154 and 156, respectively, are generally operable to two positions as schematically illustrated in FIG. 1.

The first isolation valve 154 has a first port 154A in selective fluid communication with the primary output conduit 136, while the primary output conduit 136 itself is in fluid communication with the primary output pressure chamber 142. The second port 154B of the first isolation valve 154 is in selective fluid communication with a boost conduit 158. The third port 154C of the first isolation valve 154 is in fluid communication with the conduit 160, and the conduit 160 itself is in selective fluid communication with the first and fourth wheel brakes 106A and 106D, respectively.

The second isolation valve 156 has a first port 156A, the first port 156A being in selective fluid communication with the secondary output conduit 138, the secondary output conduit 138 itself being in fluid communication with the secondary output pressure chamber 140. The second port 156B of the second isolation valve 156 is in selective fluid communication with a pressurization conduit 158. The third port 156C of the second isolation valve 156 is in fluid communication with a conduit 178, which conduit 178 is itself in selective fluid communication with the second and third wheel brakes 106B and 106C, respectively.

The service braking system 100 also includes various valves, i.e., slip control valve arrangements, for allowing controlled braking operations, such as ABS, traction control, vehicle stability control, and regenerative braking blending. The first set of valves includes a first apply or inlet valve 162 and a first exhaust or outlet valve 164 in fluid communication with the conduit 160 for cooperatively supplying brake fluid received from the booster valve to the fourth wheel brake 106D and for cooperatively exhausting pressurized brake fluid from the fourth wheel brake 106D to a first reservoir conduit 166, the first reservoir conduit 166 being in fluid communication with a second reservoir conduit 168 to the fluid reservoir 108. The second set of valves includes a second apply or inlet valve 170 and a second drain or outlet valve 172 in fluid communication with the conduit 160 for cooperatively supplying brake fluid received from the boost valve to the first wheel brakes 106A and for cooperatively draining pressurized brake fluid from the first wheel brakes 106A to the first reservoir conduit 166. The third set of valves includes a third apply or inlet valve 174 and a third drain or outlet valve 176 in fluid communication with a conduit 178 for cooperatively supplying brake fluid received from the boost valves to the third wheel brakes 106C and for cooperatively draining pressurized brake fluid from the third wheel brakes 106C to the first reservoir conduit 166. The fourth set of valves includes a fourth apply or inlet valve 180 and a fourth exhaust or outlet valve 182 in fluid communication with the conduit 178 for cooperatively supplying brake fluid received from the boost valve to the second wheel brakes 106B and for cooperatively exhausting pressurized brake fluid from the second wheel brakes 106B to the first reservoir conduit 166.

As described above, the service braking system 100 includes a pressure source in the form of a plunger assembly 152 to provide a desired pressure level to the first, second, third and fourth wheel brakes 106A, 106B, 106C, 106D, respectively. Service braking system 100 also includes a vent valve 184 and a pump valve 186 that cooperate with plunger assembly 152 to provide boost pressure to boost conduit 158 to actuate first wheel brake 106A, second wheel brake 106B, third wheel brake 106C, and fourth wheel brake 106D, respectively. The vent valve 184 and the pump valve 186 may be solenoid actuated valves movable between open and closed positions. In the closed position, as schematically illustrated in fig. 1 as a check valve, the vent valve 184 and the pump valve 186 may still allow flow in one direction. The vent valve 184 is in fluid communication with the second reservoir conduit 168, and the first output conduit 188 is in fluid communication with the plunger assembly 152. A second output conduit 190 is in fluid communication between the plunger assembly 152 and the pressurization conduit 158.

The plunger assembly 152 includes a piston 192, generally indicated by reference numeral 194, connected to a ball screw mechanism. The ball screw mechanism 194 is provided to impart translational or linear movement of the piston 192 along an axis in both a forward direction (rightward when viewing fig. 1) and a rearward direction (leftward when viewing fig. 1). The ball screw mechanism 194 includes a motor 196 that rotatably drives a screw shaft 198. The motor 196 may include a sensor for detecting the rotational position of the motor 196 and/or the ball screw mechanism 194. The rotational position represents the linear position of the piston 192. Plunger assembly 152 also includes a first pressure chamber 200 and a second pressure chamber 202.

As described above, the brake pedal unit assembly 102 includes the analog valve 126. As schematically shown in fig. 1, the analog valve 126 may be a solenoid-actuated valve. The analog valve 126 includes a first port and a second port. The first port is in fluid communication with the conduit 134, and the conduit 134 itself is in fluid communication with the fluid simulation chamber 132. The second port is in fluid communication with the conduit 128, and the conduit 128 itself is in fluid communication with the fluid reservoir 108 through the conduit 124. The simulation valve 126 is movable between a first position restricting fluid flow from the fluid simulation chamber 132 to the fluid reservoir 108 and a second position allowing fluid flow between the fluid reservoir 108 and the fluid simulation chamber 132. When not actuated, as will be described in greater detail below, the simulation valve 126 is in a first or normally closed position, thereby preventing fluid from flowing out of the fluid simulation chamber 132 through the conduit 128.

The service braking system 100 is also provided with a system status sensor 204 which provides a system status for the service braking system 100. For example, the system status sensor 204 may provide a system status that the plunger assembly 152 has failed or is otherwise unavailable, or that the service brake system 100 is operating in a propel or manually applied mode (the propel mode will be discussed further).

The vehicle also has first and second Electric Parking Brakes (EPBs), generally indicated by reference numerals 206A and 206B, respectively. The general structure and operation of the first EPB206A and the second EPB206B, respectively, are conventional in the art. Accordingly, only those portions of first EPB206A and second EPB206B that are necessary for a complete understanding of the present invention will be explained in detail. For example, first EPB206A and second EPB206B may each be as disclosed in U.S. Pat. No.8,844,683 to Sternal et al, the disclosure of which is incorporated herein by reference in its entirety. Unless otherwise specified, the discussion of one of the first or second EPBs 206A or 206B, respectively, applies to the other of the first or second EPBs 206A or 206B, respectively.

As shown, the first EPB206A is disposed at the third wheel brake 106C and the second EPB206B is disposed at the fourth wheel brake 106D. Preferably, when the first EPB206A is disposed at the third wheel brake 106C and the second EPB206B is disposed at the fourth wheel brake 106D, the third wheel brake 106C and the fourth wheel brake 106D are respectively located on the rear axle of the vehicle. Alternatively, there may be more or less than first EPB206A and second EPB206B provided for the vehicle, respectively. Alternatively, the third wheel brake 106C and the fourth wheel brake 106D may be respectively not on the rear axle or on the same axle.

A first driver 208 is provided for the first EPB 206A. Similarly, a second driver 210 is provided for the second EPB 206B. Preferably, the first and second drivers 208 and 210, respectively, are motors. The first driver 208 is operable to selectively support the brake piston of the third wheel brake 106C on the brake rotor 304 mounted on the associated wheel. Similarly, the second drive 210 is operable to selectively support the brake piston of the fourth wheel brake 106D on the brake rotor 304 on another associated wheel. As such, the first and second EPBs 206A and 206B, respectively, are motor caliper (MOC) type EPBs, and the third and fourth wheel brakes 106C and 106D, respectively, may be electrically driven. Normal operation of first EPB206A and second EPB206B provides a parking brake function for the vehicle, respectively.

In addition to the system state sensors 204, a brake Electronic Control Unit (ECU)212, a parking brake Electronic Control Unit (ECU)218, a parking brake manual controller 220, and an accelerator pedal input sensor 222 are provided. The brake ECU212, the parking brake ECU 218, the parking brake manual controller 220, and the accelerator pedal input sensor 222 will be further discussed. The system state sensors 204, the brake ECU212, the parking brake ECU 218, the parking brake manual controller 220, and the accelerator pedal input sensor 222 are connected by a data bus 224. The data bus 224 also connects the brake pedal unit assembly 102 and the first and second EPBs 206A and 206B, respectively. An accelerator input sensor 222 measures an accelerator input that controls vehicle propulsion.

The following is a description of the normal operation of the service brake system 100 in the hydraulic boost brake-by-wire mode. Alternatively, the service braking system may be a hydraulic boost system, but not in the brake-by-wire mode. Fig. 1 shows the service brake system 100 and the brake pedal unit 112 in a rest position. In this case, the driver does not depress the service brake pedal 120. Also in the quiescent state, the analog valve 126 may be energized or de-energized. During a typical braking condition, the service brake pedal 120 is depressed by the driver. Service brake pedal 120 is coupled to a stroke sensor 144 for generating a pedal stroke signal indicative of the stroke length of input piston 114 and providing the pedal stroke signal to brake ECU 212.

The brake ECU212 may include a microprocessor. The brake ECU212 receives various signals, processes the signals, and controls the operation of various electrical components of the service braking system 100 in response to the received signals. The control module may be connected to various sensors such as pressure sensors, travel sensors, switches, wheel speed sensors, and steering angle sensors. The brake ECU212 may also be connected to an external module (not shown) for receiving information relating to the yaw rate, lateral acceleration, longitudinal acceleration of the vehicle, for example for controlling the service braking system 100 during vehicle stability operation.

In addition, the brake ECU212 may be connected to an instrument panel for collecting and providing information related to warning indicators such as an ABS warning lamp, a brake fluid level warning lamp, and a traction control/vehicle stability control indicator lamp.

During normal braking operation (normal boost apply braking operation), the plunger assembly 152 operates to provide boost pressure to the boost conduit 158 for actuating the first, second, third and fourth wheel brakes 106A, 106B, 106C and 106D, respectively. Under certain driving conditions, the brake ECU212 communicates with a powertrain control module (not shown) and other additional brake controllers of the vehicle to provide coordinated braking during advanced brake control schemes such as anti-lock braking (AB), Traction Control (TC), Vehicle Stability Control (VSC), and regenerative braking blending. During normal boost apply brake operation, a flow of pressurized fluid from the brake pedal unit 112 is generated by depressing the service brake pedal 120 and is diverted into the internal pedal simulator assembly 130. The simulation valve 126 is actuated to divert fluid from the fluid simulation chamber 132 through the simulation valve 126 to the fluid reservoir 108 via conduits 124, 128, and 134. Prior to movement of the input piston 114, as shown in fig. 1, the fluid simulation chamber 132 is in fluid communication with the fluid reservoir 108 via the conduit 124.

During the duration of the normal braking mode, the simulation valve 126 remains open to allow fluid to flow from the fluid simulation chamber 132 to the fluid reservoir 108. The fluid within the fluid simulation chamber 132 is non-pressurized and is at a very low pressure, such as atmospheric pressure or a low reservoir pressure. The advantage of this non-pressurized configuration is that the sealing surface of the pedal simulator is not subjected to the high friction of the seal acting on the surface due to the high pressure fluid. In conventional pedal simulators, as the brake pedal is depressed, the pistons are under increasingly higher pressure, so that they are subjected to large frictional forces from the seals, thereby adversely affecting pedal feel.

Also during normal boost apply braking operation, the first and second isolation valves 154 and 156, respectively, are energized to the secondary position to prevent fluid flow from the primary and secondary output conduits 136 and 138, respectively, through the first and second isolation valves 154 and 156, respectively. Fluid is prevented from flowing from first port 154A to third port 154C and from first port 156A to third port 156C. Thus, the fluid within the primary and secondary output pressure chambers 142, 140 of the brake pedal unit 112 is fluidly locked, which generally prevents further movement of the primary and secondary pistons 116, 118, respectively.

More specifically, during an initial phase of a normal boost apply brake operation, movement of the input rod 122 causes movement of the input piston 114 in a rightward direction, as viewed in FIG. 1. Initial movement of the input piston 114 causes movement of the master piston 116. The movement of the primary piston 116 causes an initial movement of the secondary piston 118 due to the mechanical connection therebetween. Also, during initial movement of the second piston 118, fluid is free to flow from the secondary pressure chamber 140 to the fluid reservoir 108 via conduits 214 and 216 until conduit 155 has moved sufficiently to the right to close conduit 214.

After the primary and secondary pistons 116 and 118, respectively, stop moving, the input piston 114 continues to move to the right (as shown in FIG. 1), moving further as the driver depresses the service brake pedal 120. Further movement of the input piston 114 compresses the various springs of the pedal simulator assembly 130, thereby providing a feedback force to the driver of the vehicle.

During normal braking operation (normal boost apply braking operation), when the pedal simulator assembly 130 is driven by depressing the service brake pedal 120, the plunger assembly 152 may be driven by the electronic control unit to provide drive to the first, second, third and fourth wheel brakes 106A, 106B, 106C, 106D, respectively. The first and second isolation valves 154 and 156, respectively, are driven to their secondary positions to prevent fluid flow from the primary and secondary output conduits 136 and 138, respectively, through the first and second isolation valves 154 and 156, respectively, and to isolate the brake pedal unit 112 from the first, second, third and fourth wheel brakes 106A, 106B, 106C and 106D, respectively. The plunger assembly 152 may provide a "boost" or higher pressure level to the first, second, third and fourth wheel brakes 106A, 106B, 106C, 106D, respectively, as compared to the pressure generated by the brake pedal unit 112 via the driver depressing the service brake pedal 120. Thus, the service braking system 100 provides auxiliary braking that provides boost to the first, second, third and fourth wheel brakes 106A, 106B, 106C, 106D, respectively, during normal boost apply braking operations, which helps reduce the force required by the driver to act on the service brake pedal 120.

When in its rest position (as shown in fig. 1), the first, second, third and fourth wheel brakes 106A, 106B, 106C, 106D, respectively, are actuated by the plunger assembly 152, and the electronic control unit energizes the vent valve 184 to its closed position (as shown in fig. 1). The vent valve 184 in the closed position prevents fluid from passing to the fluid reservoir 108 by flowing from the first output conduit 188 to the second reservoir conduit 168. The pump valve 186 is de-energized to its open position (shown in fig. 1) to allow fluid to flow through the pump valve 186.

The electronic control unit drives the motor 196 in a first rotational direction to rotate the screw shaft 198 in the first rotational direction. Rotation of the screw shaft 198 in a first rotational direction advances the piston 192 in a forward direction (to the right when viewing fig. 1). Movement of the piston 192 causes the pressure in the first pressure chamber 200 to increase and fluid flows out of the first pressure chamber 200 and into the first output conduit 188. Fluid may flow into the pressurization conduit 158 through the open pump valve 186. Note that when the piston 192 advances in the forward direction, fluid is allowed to flow into the second pressure chamber 202 via the second output conduit 190.

Pressurized fluid from the pressurization conduit 158 is directed through the first and second isolation valves 154 and 156 into conduits 160 and 178, respectively. Pressurized fluid from conduits 160 and 178 may be directed to first wheel brake 106A, second wheel brake 106B, third wheel brake 106C, and fourth wheel brake 106D, respectively, through open first, second, third, and fourth apply valves 162, 170, 174, and 180, respectively, while first, second, third, and fourth exhaust valves 164, 172, 176, and 182, respectively, remain closed. When the driver releases the service brake pedal 120, pressurized fluid from the first, second, third and fourth wheel brakes 106A, 106B, 106C, 106D, respectively, may drive the ball screw mechanism 194 rearwardly, moving the piston 192 rearwardly to its rest position. In some instances, it may also be desirable to drive the motor 196 of the plunger assembly 152 to retract the piston 192 and draw fluid from the first, second, third and fourth wheel brakes 106A, 106B, 106C, 106D, respectively. During the forward stroke of plunger assembly 152, pumping valve 186 may be in its open position or remain closed.

During a braking event, the electronic brake ECU212 may also selectively actuate the first, second, third and fourth apply valves 162, 170, 174 and 180, respectively, and the first, second, third and fourth exhaust valves 164, 172, 176 and 182, respectively, to provide the desired pressure levels to the fourth, first, third and second wheel brakes 106D, 106A, 106C and 106B, respectively.

In some instances, the piston 192 of the plunger assembly 152 may reach its full stroke length on the forward stroke and it may still be desirable to transfer additional boost force to the first, second, third, and fourth wheel brakes 106A, 106B, 106C, 106D, respectively. Plunger assembly 152 is a dual-acting plunger assembly such that it is configured to also provide boost pressure to boost conduit 158 as piston 192 travels rearward. This has the advantage over conventional plunger assemblies that first require their pistons to be brought back to their resting or retracted positions before they again advance the pistons to create pressure within the individual pressure chambers.

For example, if the piston 192 has reached its full stroke and still requires additional pressurization force, the pumping valve 186 is energized to its closed check valve position. The vent valve 184 may be de-energized to its open position. Alternatively, the vent valve 184 may remain energized in its closed position to allow fluid to flow through its check valve during the pumping mode. The electronic control unit drives the motor 196 in a second rotational direction opposite the first rotational direction to rotate the screw shaft 198 in the second rotational direction. Rotation of the screw shaft 198 in a second rotational direction causes the piston 192 to retract or move in a rearward direction (to the left when viewing fig. 1). Movement of the piston 192 causes the pressure in the second pressure chamber 202 to increase and fluid flows out of the second pressure chamber 202 and into the second output conduit 190. Note that when the piston 192 moves rearward or on its return stroke, fluid is allowed to flow into the first pressure chamber 200 via the second reservoir conduit 168 and the first output conduit 188.

Pressurized fluid from the pressurization conduit 158 is directed through the first and second isolation valves 154 and 156 into conduits 160 and 178, respectively. Pressurized fluid from conduits 160 and 178 may be directed to first wheel brake 106A, second wheel brake 106B, third wheel brake 106C, and fourth wheel brake 106D, respectively, through open first, second, third, and fourth apply valves 162, 170, 174, and 180, respectively, while first, second, third, and fourth exhaust valves 164, 172, 176, and 182, respectively, remain closed. In a similar manner to during the forward stroke of piston 192, brake ECU212 may also selectively actuate first, second, third and fourth apply valves 162, 170, 174 and 180, respectively, and first, second, third and fourth exhaust valves 164, 172, 176 and 182, respectively, to provide the desired pressure levels for fourth, first, third and second wheel brakes 106D, 106A, 106C and 106B, respectively.

In the event of a loss of electrical power to portions of the service brake system 100 (such that the normal boost operating mode is not active or available), the service brake system 100 provides operation in a manual propulsion or manual apply mode such that the brake pedal unit 112 may supply relatively high pressure fluid to the primary and secondary output conduits 136, 138. During an electrical fault, motor 196 of plunger assembly 152 may cease to operate, thereby failing to generate pressurized hydraulic brake fluid from plunger assembly 152. First and second isolation valves 154 and 156 will shuttle (or remain) in their positions, respectively, to allow fluid flow from primary and secondary output conduits 136 and 138, respectively, to first, second, third, and fourth wheel brakes 106A, 106B, 106C, and 106D, respectively. The simulation valve 126 is shuttled to its closed position to prevent fluid from flowing out of the fluid simulation chamber 132 to the fluid reservoir 108. Thus, moving the simulation valve 126 to its closed position hydraulically locks the fluid simulation chamber 132 and traps fluid therein. During manual advancement application, primary piston 116 and secondary piston 118 will advance to the right, respectively, to pressurize secondary chamber 140 and primary chamber 142, respectively. Fluid flows from secondary chamber 140 and primary chamber 142 into primary output conduit 136 and secondary output conduit 138, respectively, to actuate first wheel brake 106A, second wheel brake 106B, third wheel brake 106C, and fourth wheel brake 106D, respectively, as described above.

During manual boost application, initial movement of the input piston 114 forces the springs of the pedal simulator to begin moving the primary piston 116 and the secondary piston 118, respectively. After further movement of the input piston 114, wherein fluid within the fluid simulation chamber 132 is trapped or hydraulically locked, further movement of the input piston 114 pressurizes the fluid simulation chamber 132. This causes movement of the primary piston 116, which also causes movement of the secondary piston 118 due to pressurization of the primary output pressure chamber 142.

As shown in fig. 1, the diameter of the input piston 114 is smaller than the diameter of the master piston 116. Because the hydraulically effective area of the input piston 114 is less than the hydraulically effective area of the master piston 116, the input piston 114 may travel axially more in the right-hand direction (when viewing FIG. 1) than the master piston 116. The advantage of this configuration is that although the reduced diameter effective area of the input piston 114 requires further travel than the larger diameter effective area of the master piston 116, the force input by the driver's foot is reduced. Thus, the force that the driver needs to act on the service brake pedal 120 to pressurize the first, second, third and fourth wheel brakes 106A, 106B, 106C, 106D is small compared to a system in which the input piston 114 and the master piston 116 have the same diameter.

In another example of a malfunction or fault condition of the service brake system 100, the hydraulic control unit 104 may fail as described above, and in addition one of the primary and secondary output pressure chambers 142 and 140 may be reduced to zero or reservoir pressure, respectively, such as a seal failure or a leak in one of the primary or secondary output conduits 136 or 138. The mechanical coupling of the primary piston 116 and the secondary piston 118 prevents a large gap or distance between the primary piston 116 and the secondary piston 118, respectively, and prevents having to advance the primary piston 116 and the secondary piston 118, respectively, over a relatively large distance without increasing the pressure in the non-faulted circuit. For example, if the service braking system 100 is in a manual propulsion mode, and additionally a loss of fluid pressure in the output circuit (e.g., in the secondary output conduit 138) occurs relative to the secondary piston 118, the secondary piston 118 will be forced or deflected in a rightward direction due to the pressure within the primary output pressure chamber 142.

If the primary and secondary pistons 116 and 118, respectively, are not connected together, the secondary piston 118 will be free to travel to its right-most position (as shown in FIG. 1), and the driver must depress the service brake pedal 120 a distance to compensate for this travel loss. However, because the primary piston 116 and the secondary piston 118 are connected together by the locking members, respectively, such movement of the secondary piston 118 is prevented, and relatively little loss of travel occurs in this type of failure. Thus, if the secondary piston 118 is not connected to the primary piston 116, the maximum volume of the primary output pressure chamber 142 is limited.

In another example, if the service braking system 100 is in a manual propulsion mode, and additionally there is a loss of fluid pressure in the output circuit (e.g., in the main output conduit 136) relative to the primary piston 116, the secondary piston 118 will be forced to deflect in a left direction or a leftward direction due to the pressure within the secondary output pressure chamber 140. Due to the configuration of brake pedal unit 112, the left-hand end of secondary piston 118 is relatively close to the right-hand end of primary piston 116. Therefore, the movement of the secondary piston 118 toward the primary piston 116 is reduced during such pressure loss, as compared to a conventional master cylinder in which the primary piston 116 and the secondary piston 118 each have the same diameter and are slidably disposed in the same bore. To achieve this advantage, the housing of the brake pedal unit 112 includes a stepped bore arrangement such that the diameter of the second bore that receives the master piston 116 is greater than the diameter of the third bore that receives the second piston 118. A portion of the primary output pressure chamber 142 includes an annular region around the left hand portion of the second piston 118 so that the primary and secondary pistons 116 and 118, respectively, may be maintained relatively close to each other during manual plunging operations.

In the illustrated construction, the primary piston 116 and the secondary piston 118 travel together during a manual pushing operation, respectively, wherein the two circuits corresponding to the primary output conduit 136 and the secondary output conduit 138, respectively, are complete. This same travel speed is attributed to the hydraulically effective areas of the primary and secondary pistons 116 and 118, respectively, because their respective primary and secondary output pressure chambers 142 and 140, respectively, are approximately equal. In a preferred embodiment, the diametric area of the secondary piston 118 is approximately equal to the area of the diameter of the primary piston 116 minus the diameter of the secondary piston 118. Of course, brake pedal unit 112 may be configured differently such that primary piston 116 and secondary piston 118 each travel at different speeds and distances during a manual propel operation.

Referring now to FIG. 2, the third wheel brake 106C with the first drive 208 of the first EPB206A is shown in detail. The discussion of the third wheel brake 106C and the first driver 208 also applies to the fourth wheel brake 106D having the second EPB206B and the second driver 210 of any other EPB that may be provided. Furthermore, the discussion of the third wheel brake 106C without the first actuator 208 also applies to the first and second wheel brakes 106A and 106B, respectively. The third wheel brake 106C and the first drive 208 together comprise a disc brake device, generally indicated by reference numeral 300.

The third wheel brake 106C comprises a brake caliper assembly 302, the brake caliper assembly 302 being mounted in a floating manner by means of a brake spider (not shown) in a known manner and spanning a brake rotor 304, which brake rotor 304 is coupled to the wheel in a rotationally fixed manner. A brake pad arrangement is provided in the brake caliper assembly 302 having a first brake pad 306 supported on the brake caliper assembly 302 and a second brake pad 308 supported on a brake piston 310. The first brake pad 306 and the second brake pad 308 respectively face each other and, in the illustrated released position, a small air gap is provided on both sides of the brake rotor 304 so that no significant braking force or other residual resistive torque occurs. A second brake pad 308 is disposed on the brake piston 310 for common movement by means of a brake pad carrier 310. A brake piston 310 is movably mounted in a fluid chamber 312 in the brake caliper assembly 302. The third wheel brake 106C may be hydraulically driven by the driver via a brake pedal 120 or by the hydraulic control unit 104. The third wheel brake 106C is hydraulically driven by operating the third apply valve 174 to supply fluid pressure to the fluid chamber 312 via the conduit 314. The fluid pressure moves the brake piston 310 to the left in fig. 2 such that the first brake block 306 and the second brake block 308 (the first brake block 306 via the brake caliper assembly 302) respectively engage the brake rotor 304.

In addition, it can be seen in fig. 2 that the brake piston 310 is realized hollow. The thrust piece 316 of the first driver 208 is accommodated in the brake piston 310. The first driver 208 also includes a drive assembly 318 having a motor and transmission. An output shaft 320 of the drive assembly 318 drives a drive shaft 322, the drive shaft 322 being supported by an axial bearing 324 and threadedly received in a threaded receiver 326 of the thrust member 316.

In the region facing the brake rotor 304 on the left in fig. 2, the thrust piece 316 has a conical portion 328, which conical portion 328 can form a bearing contact with a complementary conical inner surface 330 of the brake piston 310. In the released position shown in fig. 2, there is a gap 332 between the two tapered surfaces 328 and 330. Accordingly, a gap 332 is located between the driver 208 and the brake piston 310.

The parking brake ECU 218 (shown in fig. 1) controls the operations of the first EPB206A and the second EPB206B, respectively. When the first EPB206A is normally applied, the brake piston 310 of the third wheel brake 106C is displaced by fluid pressure (via the service brake system 100) such that the first brake pad 306 and the second brake pad 308 of the third wheel brake 106C are respectively pressed into engagement with the brake rotor 304 mounted on the associated wheel. Thus, the brake piston 310 includes a hydraulic drive mechanism. Subsequently, the first actuator 208 is operated such that the brake piston 310 is supported on the first actuator 208 against the brake rotor 304. The fluid pressure may then be removed and the brake piston 310 may remain supported on the first driver 208. Thus, the first and second drivers 208 and 210, respectively, comprise an electric drive mechanism. When the first EPB206A is normally released, fluid pressure is reapplied (if removed during application of the first EPB 206A), the first actuator 208 is operated such that the brake piston 310 is no longer supported on the first actuator 208, and then the fluid pressure is released to allow the first brake block 306 and the second brake block 308, respectively, to release from the brake rotor 304. Alternatively, the first actuator 208 may operate to support the brake piston 310 on the first actuator 208 against the brake rotor 304 without the brake piston 310 being first displaced by fluid pressure. The normal operation of the second EPB206B is similar to the first EPB 206A.

The first driver 208 and the second driver 210 each generate a variable amount of torque. As the amount of torque increases, the braking forces generated by first EPB206A and second EPB206B, respectively, also increase, and as the amount of torque decreases, the braking forces generated by first EPB206A and second EPB206B, respectively, also decrease. Thus, each of first EPB206A and second EPB206B may be applied or released between full release and full application, respectively. First and second actuators 208 and 210 may each be independently controlled such that each of first and second EPBs 206A and 206B, respectively, generates a different braking force.

The parking brake ECU 218 may control the first EPB206A and the second EPB206B, respectively, in response to a parking brake manual controller 220 (shown in fig. 1). As a non-limiting example, parking brake input manual control 220 may be a button, switch, or lever by which the driver of the vehicle applies or releases first EPB206A and second EPB206B, respectively.

Referring now to FIG. 3, a first embodiment of a control method (generally designated by reference numeral 350) is shown for service brake system 100 and first and second EPBs 206A and 206B, respectively. Control method 350 operates first EPB206A and second EPB206B, respectively, to provide deceleration, i.e., braking, to the vehicle in response to a service braking demand from service brake pedal 120. Control method 350 limits travel of service brake pedal 120 during certain boost failure conditions. Control method 350 is preferably performed when the system status indicates a fault condition. Thus, the control method 350 bypasses the parking brake ECU 218.

In step S101, the control method 350 checks whether the entry condition is satisfied. The entry conditions preferably include, but are not limited to, the system status sensor 204 indicating a fault condition for the service brake system 100, the first and second EPBs 206A and 206B, respectively, being operating normally, the first and third exhaust valves 164 and 176, respectively, remaining operable and controllable to isolate the third and fourth wheel brakes 106C and 106D, respectively, and the first and second pressure sensors 148 and 150, respectively, being responsive. As discussed, the fault condition may be that the service brake system 100 is operating in a propulsion mode and the boost fails. Typically, this is the result of a failure of the motor 196. When the entry condition is satisfied, the control method 350 proceeds to step S102. When the entry condition is not satisfied, the control method 350 repeats step S101 until the entry condition is satisfied. Preferably, the entry conditions are checked throughout the control method 350, and if the entry conditions are no longer satisfied, the control method 350 aborts.

In step S102, the control method 350 checks whether the service brake pedal 120 is being depressed or whether there is an initial braking command to run the first EPB206A and the second EPB206B, respectively. Preferably, step S102 checks whether the service brake pedal 120 is being depressed more than the minimum stroke amount. When the service brake pedal 120 is depressed, the control method 350 proceeds to step S103. When the service brake pedal 120 is not depressed, the control method 350 returns to step S101. A duration may be set after which control method 350 returns to step S101 if service brake pedal 120 is not depressed. Alternatively, step S102 may be repeated until service brake pedal 120 is depressed.

In the event that the entry condition is met and the service brake pedal 120 is depressed, in step S103 the third wheel brake 106C and the fourth wheel brake 106D with the first EPB206A and the second EPB206B, respectively, are isolated, for example hydraulically isolated. Isolating the third and fourth wheel brakes 106C and 106D, respectively, retains only fluid pressure. This will result in a travel of the service brake pedal 120 that is less than the travel resulting from the four-wheel propulsion mode.

As shown, isolating the third wheel brake 106C and the fourth wheel brake 106D, respectively, requires that the third wheel brake 106C and the fourth wheel brake 106D, respectively, be isolated. As discussed, the third wheel brake 106C is isolated by closing the third apply valve 174 and the third exhaust valve 176. Similarly, fourth wheel brake 106D is isolated by closing fourth apply valve 180 and fourth exhaust valve 182. The isolation of the third and fourth wheel brakes 106C and 106D, respectively, redirects the fluid pressure of the brake system 100 to the first and second wheel brakes 106A and 106B, respectively, i.e., the service brake system 100 operates in two-wheel propulsion.

In step S104, the first and second drivers 208 and 210, respectively, are operated such that the brake pads 308 contact the brake rotor 304, but the brake pads 308 are not applied to the brake rotor 304 to provide or generate any significant braking force.

In step S105, the opening time request value is calculated from the fluid pressure of the service brake system 100. The on-time request value is the duration of time to drive the first EPB206A and the second EPB206B, respectively. As a non-limiting example, the opening time request value may be calculated from the fluid pressure in the master cylinder. The calculation of the open time request value will be further discussed with reference to fig. 4A and 4B.

In step S106, the first EPB206A and the second EPB206B are run to satisfy the on-time request value, respectively, i.e., operate for a duration equal to or satisfying the on-time request value in the first EPB206A and the second EPB206B, respectively. As a result, first EPB206A and second EPB206B each generate a clamping force on brake rotor 304 such that first EPB206A is supported by first drive 208 and second EPB206B is supported by second drive 210. The braking force provides deceleration to the rear wheels of the vehicle.

In step S107, it is checked whether the exit condition of the control method 350 has been satisfied. As a non-limiting example, the exit condition may include the driver releasing the service brake pedal 120. When the exit condition has not been satisfied, the control method 350 returns to step S105. When the exit condition is satisfied, the control method 350 proceeds to step S108.

In step S108, the first EPB206A and the second EPB206B are released, respectively. When the first and second EPBs 206A and 206B, respectively, are fully released, the first and second drivers 208 and 210, respectively, are preferably operated until the feedback current is less than the post-run current threshold to ensure that the first and second drivers 208 and 210, respectively, are fully disengaged from the brake piston 310.

Then, in step S109, the wheel brake with the electric parking brake is released. As shown, this requires that the third and fourth wheel brakes 106C and 106D, respectively, be removed from isolation. The third wheel brake 106C is de-isolated by opening either the third apply valve 174 or the third exhaust valve 176 as required for operation of the service brake system 100. Similarly, the fourth wheel brake 106D is de-isolated, again as required for operation of the service brake system 100, by opening either the fourth apply valve 180 or the fourth exhaust valve 182. After step S109, the control method 350 returns to step S101.

As discussed, the control method 350 provides a deceleration when the system state sensor 204 indicates a fault state of the service brake system 100, i.e., the service brake system 100 is operating in the propel mode. Alternatively, control method 350 may operate first EPB206A and second EPB206B, respectively, to provide a deceleration rate that supplements the braking provided by service braking system 100 when there is no fault condition, i.e., when service braking system 100 is operating normally. Alternatively, control method 350 may run first EPB206A and second EPB206B, respectively, to provide deceleration that supplements other braking (e.g., engine braking). Control method 350 may run first EPB206A and second EPB206B, respectively, to provide deceleration to supplement engine braking when service brake system 100 is operating in a propulsion mode or normal.

Referring now to fig. 4A and 4B, the calculation of the on time request value of the control method 350 will be discussed. The method of calculating the on-time request value in fig. 4A and 4B is incorporated into the control method 350. For example, calculating the open time request value as in FIGS. 4A and 4B may be incorporated into step S105 of the control method 350.

As a non-limiting example, the opening time request value may be calculated based on the fluid pressure. In fig. 4A and 4B, a table generally indicated by reference numeral 352A and a graph generally indicated by reference numeral 352B show the relationship between the fluid pressure of the service brake system 100 and the opening time request value. The graph 352B shows drive time curves, generally indicated by reference numeral 353, for the first EPB206A and the second EPB206B, respectively. The on-time requirement is calibrated based on fluid pressure. Preferably, such calibration is performed on a high μ surface with various applications of service brake pedal 120. Braking performance is balanced with over-release activity on high and medium mu surfaces.

Generally, as the fluid pressure increases (indicating an increase in the application of the non-isolated first and second wheel brakes 106A and 106B, respectively), the opening time request value also increases. Thus, the braking at the rear wheels provided by the first and second EPBs 206A and 206B, respectively, is related to the braking of the service brake system 100 at the front wheels. The relationship between the fluid pressure and the opening time request value will be discussed in further detail. When the fault condition indicates a fault with the service brake system 100 and the fluid pressure is at or below the threshold value, then the control method 350 may be terminated and four-wheel propulsion may be used for the brake system 100.

The opening time request value does not increase in proportion to the fluid pressure. The on-time request value increases as the fluid pressure increases in the first and second ranges 354A and 354B, respectively, then is constant while the fluid pressure continues to increase in the third and fourth ranges 356A and 356B, respectively, and finally increases again as the fluid pressure increases in the fifth and sixth ranges 358A and 358B. The opening time request value remains constant in the third and fourth ranges 356A and 356B, respectively, reducing the likelihood that the vehicle will experience over-excitation braking, which may result in "dolphin" movement of the vehicle. As shown, a first gain is applied when calculating the on-time request values of the first range 354A, a second gain is applied when calculating the on-time request values of the second range 354B, a third gain is applied when calculating the on-time request values of the fifth range 358A, and a fourth gain is applied when calculating the on-time request values of the sixth range 358B. As further shown, the first gain is greater than the second gain, and the third gain is greater than the fourth gain. Alternatively, the first and second gains may be equal, and the third and fourth gains may be equal (such that the on-time request values will increase linearly in the first, second, fifth and sixth ranges 354A, 354B, 358A and 358B, respectively). Further, below the minimum fluid pressure 360, the on-time request value is set to zero. As shown, the minimum fluid pressure 360 is 3 bar.

The fluid pressure may be limited to discrete magnitudes or jump values such that only meaningful changes in the fluid pressure react, i.e., the opening time requirement is calculated. As a non-limiting example, the fluid pressure may be limited to discrete 5 bar values or jump values. In this case, the fluid pressure must be changed by at least 5 bar before calculating the new opening time requirement. Smaller magnitudes increase the sensitivity of the application and release to fluid pressure changes. A larger magnitude will require a greater fluid pressure before a reaction (i.e., calculation of the on-time requirement) occurs.

Alternatively, instead of the fluid pressure, the opening time request value may be calculated using a length measurement of the pedal stroke. As a non-limiting example, the measured movement of the input lever 122 may be used to calculate the open time request value. Alternatively, the measured movement of the input rod 122 may be used to check, verify, or otherwise verify the on-time requirement calculated from the fluid pressure. The measured movement of the input rod 122 may also be used to calculate a requested value for the on-time when the unavailable fluid pressure (e.g., the first and second sensors 148 or 150, respectively) is not responsive. Alternatively, the on-time request value may be calculated from the brake pedal force applied by the driver at the service brake pedal 120. Alternatively, the opening time request value may be calculated based on the fluid pressure in the plunger assembly 152.

Referring now to FIG. 5, a clearance reduction method, generally indicated by reference numeral 420, is illustrated for controlling the method 350 to reduce the clearance 332. When the throttle input sensor 222 (shown in fig. 1) indicates that the amount of change in the accelerator pedal input is greater than the minimum amount of change and the rate of change in the accelerator pedal input of the vehicle is greater than the minimum rate of change, the clearance 332 between the brake piston 310 of the third wheel brake 106C and the first driver 208 and between the brake piston 310 of the fourth wheel brake 106D and the second driver 210 may decrease. Alternatively, the gap 322 may instead be decreased upon full release of the throttle input. For the lash reduction method 420, the amount and rate of change indicate that the accelerator pedal input is decreasing, i.e., the accelerator pedal is being released. The gap reduction method 420 may be incorporated into the control method 350. For example, the gap reduction method 420 may be performed in step S204 prior to operating the first and second EPBs 206A and 206B, respectively. Alternatively, the gap reduction method 420 may be omitted from the control method 350.

In step S130, the lash reduction method 420 verifies that the control method 350 allows the first EPB206A and the second EPB206B to operate and provide deceleration for the vehicle, respectively. As a non-limiting example, step S130 may check whether step S101 in fig. 3 is yes. Alternatively, step S130 may be omitted from the gap reduction method 420.

Next, in step S131, the lash reduction method 420 checks whether the amount of change in the accelerator pedal input is greater than a minimum amount of change, and whether the rate of change in the accelerator pedal input of the vehicle is greater than a minimum rate of change. In step S132, the first and second drivers 208 and 210 may each operate to reduce the clearance 332 when the amount of change in the accelerator pedal input is greater than the minimum amount of change and the rate of change in the accelerator pedal input of the vehicle is greater than the minimum rate of change. As will be discussed, clearance 332 may be reduced to zero such that tapered surfaces 328 and 330 are in contact, but brake pad 308 is not applied to brake rotor 304. Further, when the amount of change in the accelerator pedal input is greater than the minimum amount of change and the rate of change of the accelerator pedal input of the vehicle is greater than the minimum rate of change, the vehicle is traveling in a substantially straight line, and the brake system 100 is experiencing a fault condition, the first and second drivers 208 and 210, respectively, may be operated such that the brake pads 308 contact the brake rotor 304, but the brake pads 308 are not applied to the brake rotor 304 to provide or otherwise generate any significant braking force. Preferably, the brake pads 308 are applied to the brake rotor 304 without generating any braking force.

The clearance 332 is reduced in step S132 without generating a braking demand at the service brake pedal 120, i.e. the braking demand at the service brake pedal 120 is zero during step S132. Accordingly, the clearance 332 is not reduced in step S132 such that the first brake pad 306 and the second brake pad 308 are respectively engaged with the brake rotor 304 to provide any significant braking force. Preferably, the gap 332 is reduced in step S132 without providing any braking force. When the gap 332 is zero, the brake piston 310 is in contact with the first brake pad 306 through the caliper assembly 302 and the second brake pad 308, but the first brake pad 306 and the second brake pad 308, respectively, are not engaged with the brake rotor 304 to provide any significant braking force. Preferably, when the gap 332 is zero, no braking force is generated. Reducing the gap 332 reduces the time required for the driver 310 to subsequently engage the first brake pad 306 and the second brake pad 308, respectively, with the brake rotor 304 to provide braking force. The brake pistons 310 in contact with the first brake block 306 and the second brake block 308, respectively, may be determined by monitoring the feedback current of the first driver 208 and the second driver 210, respectively.

After a duration of time, when the driver is not applying the brake pedal 120 or the accelerator pedal input returns to an applied state, the first and second drivers 208 and 210, respectively, retract to re-establish the gap 332. As a non-limiting example, the duration may be calibrated to three seconds.

In step 133, when the amount of change in the accelerator pedal input is greater than the minimum amount of change and the rate of change of the accelerator pedal input of the vehicle is greater than the minimum rate of change, the gap 332 remains in its current state and is not changed or otherwise altered by the gap reduction method 420.

Referring now to FIG. 6, a pressure relief method of the control method 350 is illustrated and generally designated by reference numeral 438. The pressure relief method 438 may be incorporated into the control method 350. For example, the pressure relief method 438 may be incorporated into step S106, which runs the first EPB206A and the second EPB206B, respectively, to meet the open time requirements and generate the clamping force.

In step S150, the pressure relief method 438 verifies that the control method 350 allows the first EPB206A and the second EPB206B to operate and provide deceleration to the vehicle, respectively. As a non-limiting example, step S150 may check whether step S101 in fig. 3 is yes. Alternatively, step S150 may be omitted from pressure relief method 438.

In step S151, the pressure relief method 438 determines whether either the first actuator 208 or the second actuator 210, respectively, is operating. In step S152, fluid pressure is allowed to flow, i.e., supply or release fluid pressure, between the fluid chamber 312 and the fluid reservoir 108, respectively, as the amount of torque generated by the first and second drivers 208 and 210, respectively, increases or decreases, i.e., the first or second drivers 208 and 210, respectively, are running or otherwise moving. By way of non-limiting example, fluid pressure may be allowed to flow between third and fourth wheel brakes 106C and 106D, respectively, by re-opening closed first and third exhaust valves 164 and 176, respectively, when first and second drivers 208 and 210, respectively, are operated to increase or decrease the amount of torque. First drain valve 164 reopens when second actuator 210 is operating and third drain valve 176 reopens when first actuator 208 is operating. In step S153, the third and fourth wheel brakes 106C and 106D, respectively, with the first and second EPBs 206A and 206B, respectively, remain isolated when the amount of torque produced by the first and second drivers 208 and 210, respectively, is not increasing or decreasing, i.e., the amount of torque remains constant and the first or second drivers 208 and 210, respectively, are not operating or moving.

The feedback current may be used to determine whether the first driver 208 or the second driver 210, respectively, is moving. When the first feedback current of the first driver 208 is greater than the idle or other minimum current, the first driver 208 is considered to be moving and the first exhaust valve 164 reopens, and the first feedback current is greater than the idle current. When the first feedback current is less than or equal to the idle current, the first driver 208 is considered to have stopped and not moving. The first discharge valve 164 is closed and the first actuator 208 is not moving. Similarly, when the second feedback current of the second driver 210 is greater than the idle or other minimum current, the second driver 210 is considered to be moving and the second bleed valve 176 is reopened, and the second feedback current is greater than the idle current. When the second feedback current is less than or equal to the idle current, the second driver 210 is considered to have stopped and not moved. The third discharge valve 176 is closed and the second actuator 210 does not move.

Only movement of the first actuator 208 or the second actuator 210 is considered during the pressure relief method 438 to determine whether to reopen the first discharge valve 164 or the third discharge valve 176, respectively. During the pressure release method 438, the direction of movement (e.g., forward or backward) of the first actuator 208 or the second actuator 210 is not considered. When the first actuator 208 or the second actuator 210, respectively, is operated to move in any direction (e.g., forward or backward), the first discharge valve 164 or the third discharge valve 176, respectively, is reopened.

It may be desirable to pair reopening of first and third discharge valves 164 and 176, respectively, to operation of first and second drivers 208 and 210 such that first and third discharge valves 164 and 176, respectively, reopen only when first and second drivers 208 and 210, respectively, are running, to avoid overheating first and third discharge valves 164 and 176, respectively. Alternatively, first and third discharge valves 164 and 176, respectively, may be open for less than the entire time that first and second actuators 208 and 210, respectively, are operating. Alternatively, during step S106 of control method 350, first and third drain valves 164 and 176, respectively, may remain open.

The clearance reduction method 420, the equivalent brake pressure calculation of fig. 4A and 4B, and the pressure release method 438 may optionally be incorporated into the control method 350. For example, all of the clearance reduction method 420, the equivalent brake pressure calculation of fig. 4A and 4B, and the pressure release method 438 may be incorporated into the control method 350. Fig. 7 illustrates a control method 350 having a clearance reduction method 420, the equivalent brake pressure calculation of fig. 4A and 4B, and a pressure release method 438 all integrated together. Alternatively, the clearance reduction method 420, the equivalent brake pressure calculation of fig. 4A and 4B, and the pressure release method 438 may not be incorporated into the control method 350. Alternatively, some combination of some of the gap reduction method 420, the equivalent brake pressure calculation of fig. 4A and 4B, and the pressure release method 438 may be incorporated into the control method 350.

Referring now to fig. 8 and 9, there is shown a second embodiment of a control method, generally indicated by reference numeral 400, and state diagrams, generally indicated by reference numeral 402, for service brake system 100 and first and second EPBs 206A and 206B, respectively. A state diagram 402 illustrates the relationship between the operating states for each of the first EPB206A and the second EPB206B, respectively, during the control method 400.

Control method 400 operates first EPB206A and second EPB206B, respectively, to provide deceleration, i.e., braking, to the vehicle in response to a service braking demand from service brake pedal 120. Preferably, the control method 400 is performed when the system status indicates a fault condition. Therefore, the control method 400 bypasses the parking brake ECU 218.

When the control method 400 has been initiated, the first EPB206A and the second EPB206B are each changed from the activated state 404 to the deactivated state 406. The control method 400 may be initiated when a key of the vehicle is turned on.

In step S201, the control method 400 checks whether the entry condition is satisfied. The entry conditions include the system state sensor 204 indicating a fault state of the service brake system 100, the first EPB206A and the second EPB206B respectively functioning normally, and the first exhaust valve 164 and the third exhaust valve 176 respectively remaining operable and controllable to isolate the third wheel brake 106C and the fourth wheel brake 106D respectively. As discussed, the fault condition may be that the service braking system 100 is operating in a propulsion mode. Typically, this is the result of a failure of the motor 196. Other entry conditions may include the driver depressing the service brake pedal 120 to indicate a braking intent. When the entry condition is satisfied, the first EPB206A and the second EPB206B each change to the preset state 408, and the control method 400 proceeds to step S202. When the entry condition is not satisfied, the control method 400 repeats step S201 until the entry condition is satisfied.

In the case where the entry condition is satisfied, in step S202, the third and fourth wheel brakes 106C and 106D having the first and second EPBs 206A and 206B, respectively, are isolated. Preferably, when the switch 146 detects a minimum amount of travel of the service brake pedal 120, the first and second EPBs 206A and 206B, respectively, are isolated. This allows the third wheel brake 106C and the fourth wheel brake 106D, respectively, to be isolated as shown. As discussed, the third wheel brake 106C is isolated by closing the third apply valve 174 and the third exhaust valve 176. Similarly, fourth wheel brake 106D is isolated by closing fourth apply valve 180 and fourth exhaust valve 182. The isolation of the third and fourth wheel brakes 106C and 106D, respectively, redirects the fluid pressure of the brake system 100 to the first and second wheel brakes 106A and 106B, respectively, i.e., the service brake system 100 operates in two-wheel propulsion.

In step S203, an equivalent brake pressure is calculated from the service brake demand, i.e. the equivalent brake pressure is mapped to the service brake demand. Preferably, the equivalent brake pressure is calculated from the fluid pressure. Alternatively, the equivalent brake pressure may be calculated from the pedal travel at service brake pedal 120 or as some other function. The calculation of the equivalent brake pressure will be further discussed with reference to fig. 10A-11B.

In step S204, the first EPB206A and the second EPB206B are operated to generate equivalent brake pressures, respectively. Specifically, first driver 208 and second driver 210 are operated to apply first EPB206A and second EPB206B, respectively. The first and second drivers 208 and 210, respectively, are operated to remove the gap 332 and bring the brake piston 310 into contact with the first brake block 306 via the caliper assembly 302 and the second brake block 308 (by moving the piston 310 to the left in fig. 2) such that the first brake block 306 and the second brake block 308, respectively, engage the brake rotor 304 to provide braking force. As a result, the first EPB206A is supported by the first drive 208, while the second EPB206B is supported by the second drive 210.

In the preset state 408, the first and second drivers 208 and 210, respectively, are synchronized to a common starting position before the first and second EPBs 206A and 206B, respectively, are operated in step S204. The first driver 208 and the second driver 210 are synchronized by running the first driver 208 and the second driver 210, respectively, until the feedback current from each of the first driver 208 and the second driver 210, respectively, is equal. Once the feedback currents are equal, the first and second drivers 208 and 210, respectively, will generate equal amounts of torque, since the amount of torque generated by the first and second drivers 208 and 210, respectively, is proportional to the feedback currents. A timer may be used to delay the measurement of the feedback current to allow the inrush current to stabilize. For example, the timer may be 120 milliseconds.

In step S204, it is checked whether the amount of torque produced by the first and second drivers 208 and 210, respectively, is decreasing, increasing or remaining constant to produce an equivalent brake pressure. As shown in FIG. 9, the first EPB206A and the second EPB206B have a hold state 410, an increased torque state 412, and a decreased torque state 414, respectively.

When the equivalent brake pressure is greater than the on-brake pressure threshold, the first EPB206A and the second EPB206B change from the hold state 410 to the increased torque state 412, respectively. In the increase torque state 412, the first and second drivers 208, 210, respectively, are operated to apply and increase the amount of torque generated by the first and second drivers 208, 210, respectively. When the equivalent brake pressure is less than the lower brake pressure threshold, the first EPB206A and the second EPB206B change from the hold state 410 to the reduced torque state 414, respectively. In the reduced torque state 414, the first and second drivers 208, 210, respectively, are operated to release and reduce the amount of torque generated by the first and second drivers 208, 210, respectively. The first EPB206A and the second EPB206B each change from the increased torque state 412 to the decreased torque state 414 when the equivalent brake pressure is less than the lower brake pressure threshold and from the decreased torque state 414 to the increased torque state 412 when the equivalent brake pressure is greater than the on-brake pressure threshold. Once first EPB206A and second EPB206B generate equivalent brake pressures, respectively, first EPB206A and second EPB206B change from increasing torque state 412 to holding state 410, or from decreasing torque state 414 to holding state 410, respectively. In the hold state 410, the first and second drivers 208, 210, respectively, are operated to hold and maintain the amount of torque currently generated by the first and second drivers 208, 210, respectively.

The upper brake pressure threshold is used for application (or partial application) of the first EPB206A and the second EPB206B, respectively, and the lower brake pressure threshold is used for release (or partial release) of the first EPB206A and the second EPB206B, respectively. The upper and lower brake pressure thresholds are set by previous operations of the first and second drivers 208 and 210, respectively, for the first and second EPBs 206A and 206B, respectively, to generate the previous equivalent brake pressures. The previous operation is from the time the first driver 208 and the second driver 210, respectively, were last energized before the control method 400 began. First and second drivers 208 and 210, respectively, may be energized during a previous execution of control method 400 or during normal operation of first and second EPBs 206A and 206B, respectively, to provide a parking brake function for the vehicle.

The upper brake pressure threshold is greater than the previous equivalent brake pressure and the lower brake pressure threshold is less than the previous equivalent brake pressure. The upper and lower brake pressure thresholds may be calibrated. For example, the upper brake pressure threshold may be 5 bar greater than the previous equivalent brake pressure, while the lower brake pressure threshold may be 5 bar less than the previous equivalent brake pressure. The upper and lower brake pressure thresholds reduce hysteresis in the control method 400.

The first and second drivers 208 and 210, respectively, may be operated to produce equal amounts of torque. Alternatively, first driver 208 and second driver 210 may be operated separately to produce unequal amounts of torque.

Although the operation of the first driver 208 and the second driver 210, respectively, has been described by the control method 400, the control method 400 may alternatively operate the first driver 208 and the second driver 210, respectively, independently. For example, the control method 400 may operate one of the first and second drivers 208 and 210, respectively, to increase the first torque amount while operating the other of the first and second drivers 208 and 210, respectively, to decrease the second torque, where the sum of the first and second torque amounts is the amount of torque that produces an equivalent brake pressure.

In step S205, it is checked whether the exit condition of the control method 400 has been satisfied. As a non-limiting example, the exit condition may include the driver releasing the service brake pedal 120. When the exit condition is not met, the control method 400 returns to step S203. When the exit condition is satisfied, the control method 400 proceeds to step S206.

In step S206, the first EPB206A and the second EPB206B are released, respectively. When the equivalent brake pressure is less than the post-run brake pressure threshold, the first EPB206A and the second EPB206B enter a post-run state 416, respectively. For example, the post-service brake pressure threshold may be 2.5 bar. When the first and second EPBs 206A and 206B, respectively, are fully released, the first and second drivers 208 and 210, respectively, are preferably operated until the feedback current is less than the post-run current threshold to ensure that the first and second drivers 208 and 210, respectively, are fully disengaged from the brake piston 310. When the feedback current is less than the post-run current threshold, the first EPB206A and the second EPB206B are each in the inactive state 406.

Then, in step S207, the wheel brakes having the electric parking brake are released. This causes the third wheel brake 106C and the fourth wheel brake 106D, respectively, to be de-isolated, as shown. The third wheel brake 106C is de-isolated by opening either the third apply valve 174 or the third exhaust valve 176 as required for operation of the service brake system 100. Similarly, the fourth wheel brake 106D is de-isolated, again as required for operation of the service brake system 100, by opening either the fourth apply valve 180 or the fourth exhaust valve 182. After step S207, the control method 400 returns to step S201. First EPB206A and second EPB206B are then each changed from post-run state 416 to inactive state 406.

As discussed, when the system state sensor 204 indicates a fault condition of the service brake system 100, the control method 400 provides a deceleration, i.e., the service brake system 100 is operating in a boost mode. Alternatively, control method 400 may operate first EPB206A and second EPB206B, respectively, to provide a deceleration rate that supplements the braking provided by service brake system 100 in the absence of a fault condition (i.e., when service brake system 100 is operating normally). Alternatively, control method 400 may operate first EPB206A and second EPB206B, respectively, to provide deceleration that supplements other braking (e.g., engine braking). Control method 400 may run first EPB206A and second EPB206B, respectively, to provide deceleration to supplement engine braking when service brake system 100 is operating in a propulsion mode or normal.

10A-11B, the calculation of the equivalent brake pressure of the control method 400 will be discussed. The method of calculating the equivalent brake pressure in fig. 10A-11B may be incorporated into the control method 400. For example, the equivalent brake pressure as calculated in FIGS. 10A-11B may be incorporated into step S203 of control method 400.

As a first non-limiting example, an equivalent brake pressure may be calculated from the fluid pressure. In fig. 10A and 10B, a first table, generally indicated by reference numeral 422A, and a first chart, generally indicated by reference numeral 422B, illustrate a first relationship between fluid pressure of the service brake system 100 and equivalent brake pressure. As the fluid pressure increases (indicating increased application of the non-isolated first and second wheel brakes 106A and 106B, respectively), the equivalent brake pressure also increases. When the fault condition indicates a fault with the service brake system 100 and the fluid pressure is at or below the threshold value, the control method 400 may be terminated and four-wheel propulsion may be used for the brake system 100.

As a second non-limiting example, the equivalent brake pressure may be calculated from the pedal travel signal. In fig. 11A and 11B, a second table, generally indicated by reference numeral 424A, and a second chart, generally indicated by reference numeral 424B, illustrate a second relationship between the pedal stroke signal and the equivalent brake pressure. As the pedal travel signal increases (indicating an increase in travel or depression of the service brake pedal 120), the equivalent braking demand also increases. As shown, the second table 424A gives the equivalent brake pressure in terms of pedal travel percentage. Alternatively, the second table 424A may give the equivalent brake pressure as a measure of the length of pedal travel.

Preferably, the pedal stroke signal is a first source for calculating an equivalent brake pressure using the fluid pressure as a backup, or a second source for calculating the equivalent brake pressure when the pedal stroke signal is unavailable. Additionally, the fluid pressure may optionally be used to check, verify, or otherwise verify the equivalent brake pressure calculated from the pedal stroke signal. As non-limiting examples, the pedal stroke signal may not be available when the switch 146 is unresponsive, and the fluid pressure may not be available when the first and second pressure sensors 148 and 150, respectively, are unresponsive. Alternatively, fluid pressure may be the first source and the pedal stroke signal the backup or second source. Alternatively, other data sources may be used to calculate the equivalent brake pressure.

Further, data inputs other than fluid pressure or pedal travel signals may be used to calculate the equivalent brake pressure. As non-limiting examples, the equivalent brake pressure may be calculated from a brake offset factor, a vehicle reference speed, a vehicle deceleration, or rear wheel slip data, in addition to the fluid pressure or pedal travel signal.

The equivalent brake pressure is not directly proportional to the brake demand (in the form of fluid pressure or pedal travel signal). Conversely, a first gain is applied when calculating the equivalent brake pressure for a first range 426 of the pedal stroke signal (for a first range of travel of service brake pedal 120), a second gain is applied when calculating the equivalent brake pressure for a second range 428 of the pedal stroke signal (for a second range of travel of service brake pedal 120), and the first gain is greater than the second gain. Similarly, the third gain is applied when calculating the equivalent brake pressure for the third range 430 of fluid pressures, the fourth gain is applied when calculating the equivalent brake pressure for the fourth range 432 of fluid pressures, and the third gain is greater than the fourth gain. The first and third gains may be equal, the second and fourth gains may be equal, or a first ratio between the first and second gains may be equal to a second ratio between the third and fourth gains, although this is not required. The pedal stroke signal value in the first range 426 is less than the pedal stroke signal value in the second range 428, i.e., from rest, the travel of the service brake pedal 120 results in a pedal stroke signal beginning in the first range 426 before advancing into the second range 428. Similarly, the fluid pressure values in the third range 430 are less than the fluid pressure values in the fourth range 432. Finally, in the fifth and sixth ranges 434 and 436 of the pedal stroke signal and the fluid pressure, the equivalent brake pressure is mapped to the brake demand such that the equivalent brake pressure increases to the maximum equivalent brake pressure at a constant rate. As a non-limiting example, the maximum equivalent brake pressure may be the maximum allowable fluid pressure allowed or able to be generated by the service brake system 100.

Below a minimum equivalent brake pressure, e.g., 0.5 bar for the fluid pressure in fig. 10A or 5% for the pedal stroke signal in fig. 11A, the control method 400 is inhibited from operating the first EPB206A and the second EPB206B, respectively, to provide deceleration to the vehicle. When the fault condition indicates a fault with the service brake system 100 and the control method 400 is inhibited from operating the first EPB206A and the second EPB206B, respectively, to provide deceleration for the vehicle, the service brake system 100 operates in the four-wheel propulsion mode.

Thus, first EPB206A and second EPB206B provide more braking early in the travel at the start of service brake pedal 120 braking (i.e., during first range 426 and third range 430, respectively). As a result, first EPB206A and second EPB206B are each applied more aggressively at the beginning of the travel of service brake pedal 120 than during subsequent travel of service brake pedal 120. This reduces the travel of service brake pedal 120 to achieve the driver's braking demand at service brake pedal 120.

The gap reduction method 420, the equivalent brake pressure calculation method of fig. 10A-11B, and the pressure release method 438 may be selectively incorporated into the control method 400. For example, all of the clearance reduction method 420, the equivalent brake pressure calculation method of fig. 10A-11B, and the pressure release method 438 may be incorporated into the control method 400. Fig. 12 illustrates a control method 400 having all of the gap reduction method 420, the equivalent brake pressure calculation method of fig. 10A-11B, and the pressure release method 438 combined together. Alternatively, the clearance reduction method 420, the equivalent brake pressure calculation method of FIGS. 10A-11B, and the pressure release method 438 may not be incorporated into the control method 400. Alternatively, some combination of some of the clearance reduction method 420, the equivalent brake pressure calculation method of fig. 10A-11B, and the pressure release method 438 may be incorporated into the control method 400, respectively.

The principles and modes of operation of this invention have been described and illustrated in its preferred embodiments in accordance with the provisions of the patent statutes. However, it must be understood that this invention may be practiced otherwise than as specifically explained and illustrated without departing from its spirit or scope.

Claims (11)

1. A vehicle braking system for a vehicle, comprising:

a brake pedal operable by a vehicle driver and coupled to control a brake pressure generating unit to supply hydraulic brake pressure to hydraulically-driven front and rear wheel brakes, wherein the rear wheel brakes are also configured to be electrically driven;

sensor means for monitoring driver braking intent;

the brake system is operable in a first mode in which both the front wheel brakes and the rear wheel brakes are hydraulically actuated, and a second mode in which the front wheel brakes are hydraulically actuated, and the rear wheel brakes are electrically actuated,

the rear wheel brake including a brake piston including a brake pad, and a brake caliper assembly including a brake pad operable to engage a brake rotor to brake the vehicle, the brake caliper assembly including a hydraulic drive mechanism and an electric drive mechanism,

a controller connected to the sensor arrangement for operating the electric drive mechanism to drive the rear wheel brakes in accordance with a driver's braking demand,

wherein in the second mode, the rear wheel brake is electrically driven by an electric parking brake including an actuator,

wherein in a first mode the brake piston is not supported on the drive, in a second mode the brake piston is supported on the drive, and

wherein there is a clearance between the brake piston and the actuator that decreases when the amount of change in the accelerator pedal input is greater than a minimum amount of change and the rate of change in the accelerator pedal input is greater than a minimum rate of change.

2. The braking system of claim 1, wherein the sensor device monitors brake pedal travel and the electric drive mechanism operates in accordance with brake pedal travel.

3. A braking system according to claim 1 or 2, wherein the sensor arrangement monitors a brake pedal force applied by a driver and/or a hydraulic pressure in the unit, and wherein the electric drive mechanism is operated in dependence on the pedal force and/or the hydraulic pressure.

4. A braking system according to claim 3 wherein the electrically operated mechanism operates according to a predetermined drive time profile which is a function of pedal force and/or hydraulic pressure.

5. The braking system of claim 1, wherein the controller is responsive to an initial braking command to operate the electric drive mechanism such that the brake pads move to a pad contact position.

6. The braking system of claim 5, wherein the initial braking command is a function of a stroke of the brake pedal when initially operated by a vehicle driver.

7. The braking system of claim 5, wherein the vehicle includes a vehicle accelerator pedal operable by a vehicle driver to control propulsion of the vehicle, and wherein the initial braking command is a function of the driver's rate of accelerator pedal release.

8. A braking system according to claim 1 wherein the braking system includes at least one inlet or isolation valve connected to supply pressure to the hydraulic drive mechanism and the controller is operable when the system is in the second mode to drive the isolation valve to hydraulically isolate front and rear wheel brakes.

9. A braking system according to claim 1 or 8 wherein the braking system includes at least one outlet or bleed valve connected to release pressure from the hydraulic drive mechanism and wherein the controller is operable to actuate the bleed valve during at least part of the time that the electric drive mechanism is operating to prevent hydraulic lock and/or vacuum pull in the hydraulic drive mechanism.

10. The braking system of claim 1, wherein the braking system is a brake-by-wire system, and wherein the first mode defines a brake-by-wire boost mode and the second mode defines a manual propulsion boost failure mode.

11. The brake system of claim 1, wherein the electric drive mechanism also forms part of an electric parking brake system.

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